Grass collecting cart for a riding lawn mower



FIG. 1 is a front left perspective view of a grass collecting cart for a riding lawn mower, showing our new design;

FIG. 2 is an enlarged rear perspective view thereof;

FIG. 3 is a front right perspective view thereof;

FIG. 4 is a further enlarged left side elevational view thereof. 

The ornamental design for a grass collecting cart for a riding lawn mower, as shown and described. 